Char-grill over high heat for 5 to 6 minutes on each side or until chicken is no longer pink. Remove from grill and slice each breast into 6 strips. Keep warm above 140°F.
Combine remaining ingredients (except pita breads) in bowl and mix thoroughly. Cover and chill to hold.
To assemble single serving: Place 1 pita on flat work surface. Layer ingredients across center of pita in the following order: 1/3 cup lettuce, 1 Tbsp. onions, 6 chicken strips, 2 Tbsp. cucumber-yogurt sauce and ¼ cup tomatoes.
Fold sides of pita up over filling and secure with club picks. Arrange on plate. Garnish with 3 olives and 1 dill sprig, if desired.